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Summary

This is probably one of the most useful, yet simple designs I did for the ultimaker, in addition to the XY "bananas blocks". You can read about the list of improvements on http://www.tridimake.com/2014/01/features-and-improvements-for-a-homemade-ultimaker.html
This one makes life easier for sure. Fine-tuning the level of the Z end switch is a chronic issue, especially as you switch among different nozzles or bed thicknesses.
In this design, the carriage slides tightly in two concave rails of the outer frame, which is secured on the case by four outer screws. There is NO way the carriage can move otherwise than vertically, as it should. Neither the carriage nor the micro-switch do touch the plywood for a fluid movement.
Most of what I have tried so far proved to be unreliable in this regard, probably because of something that (tried to) slide against the internal plywood wall. The only parts here that are in contact with the printer walls are the fixed parts.
I designed it for an Ultimaker, but it easily adapts to others. The openscad source code is included as usual, in case a change is needed (here is a very easy tutorial if you need it: http://www.tridimake.com/2014/09/how-to-use-openscad-tricks-and-tips-to.html)

Instructions

The main screw

I used a long M4 screw (actually a threaded rod), about 60mm long. Insert it through the hole of the top horizontal bar of the frame, then screw nuts on each side, by leaving just enough room so the whole screw + nuts rotate as a whole without any vertical play.
These nuts can be glued to the screw (as I did, after willingly damaging the thread a bit with a pair of cutting pliers), or you may use two pairs of nut and counter nut instead on each side of the top bar (as the openscan screenshot, a bulkier solution). Both ways are better that using nylocks, which would eventually slip and start to move on the thread in the long term.

Note that you could use an M3 screw for less travel per turn (in which case you'll have to change the value in the openscad source code). In my opinion, M4 is a good trade off when you change your printing bed often, because it's faster to tune with an M4.

I used my thumbnut design for the screw head, which can be customized at http://www.thingiverse.com/thing:70494 I chose small diameter and wings so that I can turn it quickly between my thumb and index fingers.

Just make sure how you mount the adjuster. The head should protrude from the top of your frame: either use a sufficiently long M4, or use a threaded rod cut at the appropriate length (as I did here in the actual device). Mine goes up a bit too much I guess. You could also use a regular screw with existing head, then use a screwdriver to tune the Z. In this case you do not even need the screw head to protrude from the top of your printer.

The carrier hole is tight, so you can screw the threaded rod directly by force (use quick forth/back movement to tap the hole when needed), but you can glue screws around or heat-sink them in the carrier if you really need it. Just make sure that the carrier slides as a nut would on the threaded rod when you rotate the latter.

The micro-switch is screwed to the carrier from the other side and though the wall of the printer. Just use screws long enough for the thickness of your printer wall. The two slabs on the carriers are there to prevent squeezing the microswitch and carrier too much against the walls, but do not tighten the screws too much (the microswitch must be allowed to slide vertically without much effort, being held by the carrier on the other side of the printer).

Finally, you can prevent lateral freeplay on the carrier thanks to the outer oblong holes on the frame. The best way to proceed is to slide the carrier at the same level as the fixing frame holes, so you know how much pinching you need before yhe screws are tightened on the printer frame. Then, move the carrier to the height of the other pair of frame screws and secure them again. Actually, no piching was required in my case, as the design is already tight (and in any case, horizontal movements have no impact on the end result, only vertical sloppiness would have).

In the end, it will only be 4 more holes in your printer frame. I did not measure the screw length, but they are quite common and you'll sort it out easily.

Hi. Actually I used threaded rod (no screw), cut to will. It is (uselessly) 60mm long as I wanted a maximal range, but 30mm may already be enough. Obviously, you get a shorter range to set the height of the microswitch, so it all depends on the variety of the beds you may use, and you need to take care of the height of the yaza gantry itself before screwing it on the printer frame (just set the carrier in the "middle" position on the printer frame, adjust the whole vertically, and mark the screws in the frame accordingly).

You also do not need that the screw head protrudes from the top of the printer if you can tune it with a screwdriver instead of a thumbwheel as I did here.

Finally, US screws could be used as long as they are approximately the same diameter (by drilling the printed part).

So I really like this design and I want to use it for my custom printer build. Have you had any issues with the screw wearing down the slider block (chariot)? It seems like you could easily make the top of the block a nut trap and put a drop of glue in there to hold it on. Or just glue it as is. A nut trap on the top part might also help.

I used it for about 2 years with no wear at all. Usually the tuning is minimalist, only when I (rarely) change the print bed itself. But I could not turn it as fast as to melt the plastic anyway even if I tried.
A captive nut could be added if you really want to make sure, but actually I favor direct threading in PLA or ABS because they leave really no play at all, which is desirable. Avoid Nylon as it tends to expand with moisture tho!
Cheers - jeremie

Printed and mounted right away, no problems at all. Works flawlessly, when my bed is a bit out of level i just crank this and its perfect again! Love it. Thanks for a simple improvement to my machine :D

I suspect you just did let the nuts loose, which you should not of course! Make sure you read the instructions: "glue them where they go after you damage the thread a bit (!)". Or you may want to glue a captive nut to the carriage if your threaded rod slips through it. I think nobody had trouble with it so far so it is weird to me ;) cheers

OK I'll try that. I Glue the 2 nuts to the carriage. I have opened up the top hole so I can use the adjuster manually by winding the nuts up or down a few turns (which is still far better than the original).

Hi Rick! You reminded me of someone years ago, and yes, you are the one who derived my end caps with a bat-symbol :D
Sorry, I am no native speaker, and this was done even before I practiced again my english ;)
Yes it really works flawlessly. Check the last picture where the yaza is fully assembled: the top two nuts should not move on the thread. They rotate as a whole with the screw. The screw itself should be able to rotate freely into the frame (top hole).
So you may glue the two nuts on the thread on each side of the frame top bar, or you can pinch (or "damage") the thread where they are located so they will not want to rotate on the screw due to friction on the top frame. You can also use pairs of nut and counter nut (locked on each other), one pair for each side of the top frame bar, as shown in the openscad overall preview (the one with colors).

Reciprocally, the central carrier hole must be tight, so it moves up or down when you rotate the screw. If you were not able to print it tight enough and the screw slips through the carrier, then you may glue a nut to the carrier (NOT to the thread of course there!). I would recommend to print it again though.

There is no screw on the carrier in my pictures because I did not need any, as the carrier hole was tight enough.

Hope you get it to work, it really made my life easier before I switched to the fully automatic "tribed" (featured on hackaday!). So in my case I need no more this convenient device. Meanwhile (=years) it really was one of the best stuff I made for the UM imho, with the banana xy blocks :)

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